The present invention relates generally to microengines or micromotors. More specifically, the invention is directed to a microengine microfabricated of polysilicon having an output gear that is rotated by synchronized linear actuators that are linked to the output gear in order to cause constant rotation of the gear, thus providing a source of torque to micro-mechanisms requiring mechanical energy. The invention is adaptable to applications involving defense, bio-medical, manufacturing, consumer products, aviation, automotive, computer (micro hard disks), inspection, and safety systems.
In the field of micromechanics, mechanical devices are of the scale of micrometers. A suitable power source for supplying continuous, constant rotational motion to other micro-mechanisms does not currently exist. There are micrometer sized electrostatic microengines that display rotational motion but are unable to drive a mechanical load. This is due to several reasons which chief among them is the inability to produce an output shaft from the microengine. Furthermore, there is great difficulty in connecting a mechanical load to the perimeter of the rotor itself because the location of stators which are used to electrostatically or electromagnetically drive the device interfere with external connections.
As explained in Mehregany et al. "Friction and Wear in Microfabricated Harmonic Side-Drive Motors", IEEE Solid State Sensor and Actuator Workshop, Hilton Head Island. S.C. June 4-7. IEEE Catalogue No. 90CH2783-9, pages 17-22, conventional microengines include a rotor pinned to a substrate or stator by a central bearing that restricts its lateral and axial motion. The entire structure shown in Mehregany was micromachined from silicon using deposition and etching steps referred to as surface micromachining in the art. The manner of energizing the rotor is via a variable-capacitance side-drive arrangement wherein stator poles are arranged about the periphery of the rotor. By appropriate energization of the side-deposited stator poles using a multiphase signal, rotation of the rotor is achieved.
The existing microengine comprises a typical center-pin bearing side-drive microengine. In this side-drive design, torque is derived via position-dependent capacitance between the rotor and stator poles. However, because of the side-by-side arrangement of the rotor and stator poles, field coupling is less than optimal and, as a result, the torque characteristics of the microengine suffer. Furthermore, the twelve stators surrounding the perimeter of the 8-pole rotor connected to the center-pin bearing make access to the rotor difficult. The rotor itself does not allow transmission of power off its perimeter because gear teeth cannot be used. Also, the center pin about which the rotor rotates is fixed and cannot serve as a shaft for power take-off.
Garcia et al., U.S. Pat. No. 5,631,514, incorporated herein by reference, discloses a microfabricated microengine that provides direct output mechanical power directly to micromechanisms without interference from the structure of the micromotor. In Garcia, however, the rotation rate of the microengine was widely variable. Garcia proposed a feedback control loop to achieve constant rotation rates; in practice, however, even the feedback control loop yielded varying rotation rates.
Thus, there is an existing need for a microengine that will provide direct output, constant rotation mechanical power directly to micromechanisms without interference from the structure of the microengine, and that can provide constant rotation rates.